Fish on Prozac

Our pharmaceutical drugs are turning up in the environment and in animals. What will the consequences be?

Over the past few years, ecologists surveying the waters around waste treatment plants have found contraceptives, synthetic musks, ibuprofen, and other compounds flushed off or out of our bodies and into the environment via municipal effluent. A recent study in Tromsø, in northern Norway, for example, found extremely elevated levels of caffeine in the seawater of the Tromsø Sound. Now the compounds are turning up in animals as well—with unknown consequences.

Environmental toxicologist Bryan Brooks and his colleagues collected bluegill, channel catfish, and black crappie from Pecan Creek, a stream in the Dallas suburb of Denton, Texas, that is prime dumping ground for effluent from the city’s waste treatment plant. The researchers took brain, liver, and muscle samples from the fish and tested them for fluoxetine, the active ingredient in the antidepressant Prozac. Fluoxetine and norfluoxetine, the metabolized form of the drug, were found in every tissue sample and in high enough concentrations, Brooks says, to warrant studies of their possible physiological effects.

Fluoxetine blocks nerves from gobbling up serotonin—a neurotransmitter known to elevate mood and increase relaxation—from the synapses between communicating neurons. In humans, the result is less anxiety and an improved sense of well-being. “We would suspect that some level of fluoxetine exposure would influence serotonin in the fish and could cause behavioral changes,” Brooks says. “It has also been shown that even low levels of pharmaceuticals may affect fish,” he says. In addition, in lab studies, other researchers found that injections of fluoxetine led to less aggressive behavior in fish. Brooks cautions, however, that “injection is a very different form of exposure than a fish taking up a chemical across its gills or acquiring it in its food. At this point it is too early to suggest that the concentrations of fluoxetine that we’ve detected might result in a behavioral response.”

Brooks and his colleagues plan to look for other pharmaceuticals in more species of fish, and they are now trying to assess the neurochemical and behavioral effects of the fluoxetine concentrations they’ve measured. The bottom line, Brooks says, “is that fish aren’t supposed to have fluoxetine in their tissues, and fluoxetine is just one of a number of pharmaceuticals that are known to be released at low levels, apparently continuously, from wastewater treatment plants, in addition to personal care products like the ingredients in fragrances and soaps. We have a very limited understanding of how all those compounds, singly or in combination, may affect organisms, and whether they are safe.”